A new 32-mer 2′,5′-oligoribonucleotide of 1-methyl-6-thioinosinic acid (10) has been synthesized. The design of this unique oligoribonucleotide is based on the reported HIV inhibitory activities of both 2′,5′-oligonucleotides and the 3′,5′-oligoribonucleotides containing the 1-methyl-6-mercaptopurine base. Tm and CD studies of 10 revealed that it has no organized secondary structure, presumably due to the rigidity of the molecule. The synthesized oligomer, 10, showed a potent inhibitory effect on HIV-1RF and significantly inhibited HIV-1 reverse transcriptase